11-ketotestosterone is not responsible for the entire testicular effect on male reproductive behaviour in the threespine stickleback

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The reproductive behaviour in the male threespine stickleback, Gasterosteus aculeatus is under androgenic control, in which 11-ketotestosterone (11KT) is the most important androgen. Previous studies have shown that castration removes reproductive behaviour, whereas treatment with 11-ketoandrostenedione (11KA), which is converted to 11KT extra-testicularily, restores all aspects of it, at least qualitatively. In this study, we investigated whether 11KT and/or testosterone (T) could restore the full magnitude of some of the more pronounced reproductive behaviours, including gluing (nest-building behaviour), zig-zagging (courtship behaviour) and displacement fanning in castrated male sticklebacks. Non-breeding males were castrated and implanted with either an empty Silastic capsule (castrated control), or a capsule containing 11KA, T or a combination of both capsules. Sham-operated males also received an empty capsule. While castrated males showed low or non-detectable plasma levels of both T and 11KT, castrated males given T or 11KA implants showed elevated levels of T and 11KT respectively, levels being within the physiological range found in intact nest-building males. Castrated males given both implants showed elevated levels of both T and 11KT. While all sham-operated males actively displayed all reproductive behaviours, these behaviours were either completely abolished or greatly reduced by castration. 11KA treated fish displayed more zig-zags and fanning than castrated fish, and unlike castrated males, built nests. Overall, 11KA or 11KA + T were more effective than T in restoring the expression of reproductive behaviours in castrated males. However, sham-operated fish displayed more gluing compared to 11KA, T and 11KA + T treated fish, and more fanning than 11KA or T treated fish. Our results indicate that 11KT and/or T cannot mediate the entire testicular effect on reproductive behaviours in the male stickleback and suggest that other testicular hormones also play a role.